(CNN) -- Venezuelan President Hugo Chavez returned unexpectedly Monday to his nation's capital, where he vowed to win the "battle for life" after undergoing emergency surgery in Cuba.

He spoke from the balcony of the presidential palace just one day before the country is set to celebrate its bicentennial.

Dressed in military fatigues and wearing a red beret, Chavez appeared in good spirits though he kept his speech uncharacteristically short -- for him -- at just over 30 minutes.

"How do I begin this conversation? The return has begun!" he said, to throngs of cheering supporters.

The president said he was under the strict supervision of doctors, eating well and exercising.

"We will win this battle for life," he said. "I put myself first in the hands of God, and second in the hands of medical science."

Perhaps tellingly, Chavez also spoke about "stages" of treatment, suggesting the fight for his health could be a long one.

"No one should think that my presence here ... means that we've won the battle," he said.

Chavez spoke as cheering supporters filled the streets around the Miraflores presidential palace, waving flags and pictures of their beloved "comandante."

"Thank you, Fidel! For taking care of him," they chanted.

Chavez, 56, returned to Venezuela unexpectedly early Monday. He had been in Cuba for weeks undergoing treatment after doctors performed emergency surgery. Chavez announced last week that they had removed a cancerous tumor.

He said then he was continuing treatment but did not specify what that treatment entailed, where the tumor was located or when he would return to Venezuela.

Prior to that announcement, the Venezuelan leader had kept a notably low profile in the three weeks since officials announced that doctors operated on him, sparking rampant rumors about his health and the country's political future.

"The speech, in some ways, was vintage Chavez," said Michael Shifter, president of the Washington-based Inter-American Dialogue, soon after the president spoke. "That magic that has enabled him to govern for 12 years hasn't disappeared."

Chavez appeared stronger than he did last week and, at least based on their reaction, has not lost the ability to inspire his supporters.

Still, the extent to which Chavez will be able to carry out his duties remains in some doubt, said Shifter, particularly given that he is up for re-election next year.

Earlier Monday, the Venezuelan leader said he did not think he would be able to accompany the vice president during official events for the nation's bicentennial Tuesday.

"But I am here, and I will be here with you from my command post in the heart of Caracas, in the heart of Venezuela," he said.

Cecilia Sosa Gomez, the former chief justice of Venezuela's Supreme Court, has said Chavez must reveal more information about his health and possibly delegate power to the vice president during his treatment.

"He has not told us what are the real effects of his situation. ... He hasn't shown how long his recuperation time is," she said before Chavez's speech, adding that his decision not to attend bicentennial festivities is significant.